Leshiy rises velocity right before regulator drops

[barreira]

Hi to all,

I wanted to change the caliber of my Leshiy .177, and I bought a .22 Diana Outlaw barrel. Being 12mm OD, only had to cut it to 320mm et voilá. Accurate as hell with Hades.

When I was rising the power through the hammer spring, I was making some readings and close to the regulator pressure (about 125-130bar) I've noticed that velocity

rise from 270m/s to 298m/s. I heard about regulator creep when the tank is full, but never when the regulator is about to drop.

Please explain this phenomenon, anyone.



Thank you

 

[JadedC]

Are you sure about the set reg pressure? The only way to be 100% sure is to test it in a reg tester since just turning the screw leaves much room for error. Is it possible that the reg is slightly higher than you originally thought and it’s coming off the reg and causing an FPS spike?

 

[Yo]

Velocity should increase when rising the power through the hammer spring.

 

[barreira]

I have the EDMU, and it indicates the set reg pressure is 120bar.

But even if if the set reg pressure is a little bit higher is it normal to spike?

 

[JadedC]

It’s normal to spike after it comes off the reg/ or when it’s close to the end of the usable pressure if the hammer spring and reg aren’t tuned in unison. If you chrony the rest of the shot string and it’s good then it’s probably something related to this.

 

[Maizen]

Yes. It’s normal.

 

[nervoustrig]

An increase in velocity around the regulator’s setpoint is an indication the hammer spring tension is set too low. As the pressure falls, the valve becomes easier to knock open and you get more lift and dwell, causing the velocity to increase. 

If you want to prevent it, increase your hammer spring tension until you find the peak velocity. Then back off until it delivers somewhere around 95 – 97% of that maximum. When you do that, the hammer strike is optimally balanced for the regulated pressure acting on the valve, and it will produce a gentle rolloff of velocity as it falls below the setpoint. You will also tend to get a better extreme spread because it is no longer operating in a state of partial valve lock.

 

[Leon83]

Something useful to read about tuning your rifles https://www.edgunwest.com/blog/2017/12/21/tuning-the-leshiy/

 

[barreira]

An increase in velocity around the regulator’s setpoint is an indication the hammer spring tension is set too low. As the pressure falls, the valve becomes easier to knock open and you get more lift and dwell, causing the velocity to increase. 

But using the HADES, the velocity is already in 277m/s / 908FPS. I get about 15 shots. Shall I rise HST even more?

 

[EDgunWest]

FYI the EDMU default is 120 bar from the factory, but your gun if it is OEM the regulator is set at 130. A properly tuned gun should be able to shoot 10 bar off the regulator, thus the EDMU is set at 120 to give an accurate shot count.

 

[barreira]

FYI the EDMU default is 120 bar from the factory, but your gun if it is OEM the regulator is set at 130. A properly tuned gun should be able to shoot 10 bar off the regulator, thus the EDMU is set at 120 to give an accurate shot count.

My gun is OEM and I hadn't mess with the regulator. Now I understand why every body says 130bar and the EDMU indicates 120bar...

Even so, is it normal such a big spike close to the regulator drop?

 

[nervoustrig]

In the event adjusting the hammer spring tension puts you above the velocity (or below the shot count) you want to have, the options are to either reduce the regulator’s setpoint or restrict the porting. Adjusting the regulator is generally preferable but if you have a power wheel (port restrictor), that’s the easy solution.

 

[barreira]

Today I did a shot string, from 237Bar filling, using Hades .22:

1. 275m/s

2. 281m/s

3. 280m/s

4. 292m/s

5. 277m/s

6. 277m/s

7. 275m/s

8. 278m/s

9. 278m/s

10. 280m/s(166Bar)

11. 288m/s(160Bar)

12. 289m/s(153Bar)

13. 293m/s(147Bar)

14. 294m/s(140Bar)

15. 294m/s(132Bar)

16. 288m/s(123Bar) 

Look at shot #4!! And the last 5 shots were almost 20m/s more than the first ones. What's wrong with my Leshiy?

Thanks in advance

 

[mike3dr]

How do you like the gun?

 

[barreira]

I like it very much, but with this kind of velocity spread it's dificult shoot accurately. 

 

[Dairyboy]

You need to lower your reg pressure it's too high for what your looking to shoot that's the issue with your reg

 

[barreira]

So you are saying with a lower pressure in the regulator I still can maintain the 277-280m/s?

 

[nervoustrig]

What is the maximum velocity you can get by increasing the hammer spring tension? That will confirm for us that there is an imbalance between the setpoint and hammer strike.

It’s such a common thing that I was quite sure it is your issue, but shot #4 above calls it into question.

 

[towle]

your setup is like the lowest gray curve, too high reg. setting for your targeted velocity

from the best explained tuning guide I have seen on the net

https://airgunguild.com/ask-bob/tuning-a-regulated-pcp/msg20336/#msg20336

 

[barreira]

your setup is like the lowest gray curve, too high reg. setting for your targeted velocity

from the best explained tuning guide I have seen on the net

https://airgunguild.com/ask-bob/tuning-a-regulated-pcp/msg20336/#msg20336

It's possible, but I didn't mess with the regulator. It is how it came from factory, from what I read, 130Bar.